Coal
Illinois ranks fourth in the nation among states that produce bituminous coal, the type of coal most widely mined in the United States. Coal is used by many manufacturing industries, by public utilities companies that burn coal to generate electricity, and by individuals for heating homes.
All Illinois coal deposits are found in the Pennsylvanian System. Of the many coals, only a few are thick enough to be mined profitably. The coal is of bituminous rank, but it varies in quality. Illinois coal reserves in strata more than 28 inches thick are estimated at 137 billion tons and are larger than those of any other state.
Around the edge of the coal basin where the coal lies at shallow depths, it is commonly mined in open pits (strip mines). However, in the past, most coal has been mined underground, and more than half of Illinois coal is still produced from such mines.